443. Transcriptomic analysis reveals differential mRNA expression in bipolar disorder
Abstract Background Bipolar disorder (BD) is a chronic and debilitating psychiatric illness characterized by recurrent episodes of mania and depression. Despite its high heritability, the underlying molecular mechanisms remain incompletely understood. Gene expression studies, particularly those focusing on total messenger RNA (mRNA), offer a promising avenue for identifying biomarkers and understanding disease pathophysiology. Among available treatments, lithium remains a first-line mood stabilizer with proven efficacy in reducing recurrence and suicide risk in BD patients. However, response to lithium is highly variable, and predictive biomarkers for treatment outcomes are lacking. Investigating total mRNA expression profiles in blood samples from BD patients characterized for lithium response may provide valuable insights into disease mechanisms and treatment response. Aims & Objectives To identify gene expression markers of disease risk and of response to lithium treatment in bipolar disorder. Method RNA sequencing was performed in a sample of 90 Caucasian patients with a diagnosis of BD type I or BD type II according to DSM-5 and 59 non-psychiatric controls with no personal or familial history of psychiatric disorders. Participants were recruited at the Unit of Clinical Pharmacology and the Unit of Clinical Psychiatry of the University of Cagliari and University Hospital Agency of Cagliari, and at the Psychiatric Hospital “Villa Santa Chiara”, Verona (Italy). For a subgroup of patients (n = 58) response to long-term lithium treatment was characterized with the Retrospective Criteria of Long-Term Treatment Response in Research Subjects with Bipolar Disorder scale (Alda scale). Total RNA was extracted from fasting peripheral venous blood samples. Library preparation and bulk RNA sequencing was performed using the Illumina Stranded Total RNA Prep, and paired-end sequencing was performed on a NextSeq 2000 platform (Illumina). After quality control, raw data were processed with the rnaseq nf-core pipeline, alignment with the reference genome (GRCh38) was performed with STAR, while gene expression levels were estimated with RSEM. Identification of differentially expressed genes (DEG) between patients and controls and responders and non-responders to lithium, adjusting for age and sex, was conducted with DESeq2. Results were adjusted for multiple testing based on false discovery rate (FDR) and an adjusted p-value < 0.05 was considered significant. Results We identified 37 DEGs between patients with BD and controls with an adjusted p-value < 0.05, of which 19 were upregulated and 18 downregulated in patients. DEG significant after multiple testing correction are reported in Table 1. DEG were enriched for the protein folding chaperone molecular function GO term (enrichment ratio: 28.79, p = 0.0002, FDR = 0.041, DNAJB1, HSP90AA1 and HSPH1). No DEG was significantly associated with lithium response after multiple testing correction. However, GO analyses on the nominally significant genes showed a significant enrichment for toll-like receptor binding molecular function GO term. Discussion & Conclusions Our study suggests that BD patients present significant differences in gene expression patterns compared to healthy controls. Pathway analyses suggest that protein misfolding and endoplasmic reticulum alterations could be implicated in the pathophysiology of BD, while response to lithium might be related to modulation of inflammatory response through toll-like receptor biding.